Various patents and devices described therein are known in the art for digitizing a graphical representation of two dimensional regions of an image having differing light values. In particular, it is known to employ coding techniques which represent linear segments by specifying the end points and thickness of the segment, as in U.S. Pat. No. 4,307,377; it is also known to code regions of differing intensity by ascertaining the branch points of boundaries of such regions, as in U.S. Pat. No. 4,189,711. It is also quite generally known to employ a piecewise linear curve fitting procedure to arrive at a digital approximation representing the boundary of a region. In order to produce a digital representation which can be utilized for computer graphics applications, such as editing and manipulation of engineering drawings, the digital representation must be sufficiently fine to represent all material dimensional features of the original; it must also represent all topological features, such as branch points. Topological data is necessary because typically at a computer graphic work station, one desires to manipulate a feature on the monitor screen, such as a girder by simply pointing to a point of its image with the cursor. This requires that post-processing software be developed which recognizes the graphic elements connected to the given point. The recognition of topological data is not easy. As a practical matter, fly specks, ink spots, and voids might easily be represented as complicated assemblies of branch points, causing a graphic digitizer to yield outputs indicative of complex topological branching. Such outputs could unnecessarily complicate the post-processing pattern recognition functions of a computer graphic system. Thus, a natural tension exists between designing a graphic digitizer which catches all significant graphic details, yet efficiently recognizes printing inperfections, and does not pass on extraneous output data related to such imperfections.